1. Field of the Invention
The present invention relates to vibration actuators and methods for manufacturing the vibration actuators. More particularly, the present invention relates to a vibration actuator including a substantially rectangular planar vibrator having a projection that serves as a friction member on one side thereof and a method for manufacturing the vibration actuator.
2. Description of the Related Art
Various vibration actuators that linearly drive driven members have been proposed. For example, U.S. Pat. No. 7,109,639 proposes a vibration-type driving apparatus. The driving principle of the apparatus will be described with reference to FIGS. 11, 12A, and 12B. Referring to FIG. 11, a vibrator 106 is provided with an electromechanical conversion device 107 bonded thereto. FIGS. 12A and 12B illustrate two bending vibration modes of the piezoelectric vibrator. The vibration mode illustrated in FIG. 12A is one of the two bending vibration modes (hereinafter called mode A). Mode A is the second-order bending mode in the long-side direction of the rectangular vibrator 106 (direction shown by arrow X), and has three nodes that are parallel to the short-side direction (direction shown by arrow Y). Projections 108 are located near the nodes of the mode A vibration, and reciprocate in the direction shown by arrow X in response to the mode A vibration. The vibration mode illustrated in FIG. 12B is the other one of the two bending vibration modes (hereinafter called mode B). Mode B is the first-order bending mode in the short-side direction of the rectangular vibrator 106 (direction shown by arrow Y), and has two nodes that are parallel to the long-side direction (direction shown by arrow X).
The nodes in mode A and the nodes in mode B are substantially orthogonal to each other in the XY plane. The projections 108 are located near the antinode of the mode B vibration, and reciprocate in the direction shown by arrow Z in response to the mode B vibration. An end portion of each projection 108 performs an ellipsoidal movement when the vibrations of mode A and mode B are generated at a predetermined phase difference. A slider 116, which serves as a driven member, is in pressure contact with the end portions of the projections 108, as shown in FIG. 11. The slider 116 can be moved in the direction shown by arrow L in response to the ellipsoidal movement of each projections 108.
In this ultrasonic motor, the driven member is brought into pressure contact with the vibrator that vibrates, so that the driven member moves relative to the vibrator in response to the vibration. Accordingly, there is a possibility that an abnormal noise will be generated as the driven member hops in response to the vibration of the vibrator. In addition, there is also a possibility that the stability of the relative movement will be reduced. To overcome these disadvantages, it is necessary to provide an elastic deformable portion that can effectively receive the vibration from the vibrator. For example, Japanese Patent Laid-Open No. 2006-174549 proposes a vibration wave driving apparatus in which spaces are provided in a surface at the side opposite to the projections, as illustrated in FIG. 13. Referring to FIG. 13, in this apparatus, a vibration actuator 207 includes a vibrator 206 and a slider 204, and the vibrator 206 includes an electromechanical conversion device 203, an elastic member 201, and projections 202 bonded to the elastic member 201. Spaces 205 are formed in a bonding surface of the elastic member 201 that is bonded to the electromechanical conversion device 203 at areas opposite to the bonding areas at which the projections 202 are bonded. The area of each space 205 is larger than the bonding area of each projection 202. Therefore, portions of the elastic member 201 at which the spaces 205 are formed function as diaphragms and are elastically deformed, thereby providing a function as springs.
In the above-described structure according to Japanese Patent Laid-Open No. 2006-174549, elastic deformable portions are provided for receiving the vibration from the vibrator. Accordingly, the abnormal noise can be somewhat reduced and the stability of the relative movement can be increased. However, this structure has the following problem. That is, since the projections are provided as separate components and are bonded to the planar elastic member, there is a risk that the projections will be slightly displaced. As a result, there is a possibility that the desired spring stiffness cannot be obtained or the desired performance cannot be achieved by the actuator. In addition, since the number of manufacturing steps is increased, high costs are incurred.